Boiler



Nov. 11, 1952 W. S. PATTERSON BOILER Filed Dec. 30, 1949 Word 8.Patterson BY ATTOR EY Patented Nov. 11, 1952 UNITED STATES PATENT OFFICECombustion Engineering-superheater,

Inc.,

New York, N. Y., a corporation of Delaware Application December 30,1949, Serial No. 137,600

2 Claims.

This invention relates in general to an improved method of burning fuelscontaining ash and to an improved construction and operation of fuelburning apparatus especially designed and particularly adapted forcarrying out this method. More specifically the present inventionrelates to a furnace arrangement of a forced circulation vaporgenerating unit.

Modern high-temperature high-capacity vapor generators are generallydivided into two classes depending on the method of ash removal. In oneclass ash is removed from the furnace in a dry state by Way of ashhoppers. In the other class of vapor generating unit the ash is removedfrom the bottom of the furnace in a fiuid state and it is this latterclass to which the present invention applies. Such so-called slaggingfurnaces are usually designed for burning bituminous or semi-bituminouscoals in a finely divided condition. In the operation of such furnacesthe gas temperature in part of the furnace is normally maintained abovethe ash fusion temperature of the fuel so that a large percentage of theash content of the fuel can be removed from the furnace chamber in amolten state.

The general object of the present invention is the provision of animproved method and apparatus for burning an ash-containing solid fuelwhich method and apparatus are characterized by a high rate of heatrelease per cubic foot of furnace volume in one or more primarychambers, a high fuel burning efiiciency, and. separation of and removalof substantially all of the recoverable ash content of the fuel in amolten condition before the combustion gas leaves the furnace.

Another object is the provision of an improved fuel burning apparatus inwhich in spite of high furnace heat release positive cooling of furnacewall surfaces is accomplished so as to permit operation at high heatabsorption rates and high steam pressure without resorting to refractoryprotection of the furnace wall tubes.

More specifically the invention is concerned with an improvedconstruction of a multi-chamber ash-slagging furnace in conjunction withforced-circulation steam generating apparatus, one object being a morecompact and space-saving furnace design.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the inventionsoperating advantages and other specific objects obtained by its use,

reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described one preferredembodiment of my invention.

Of the drawings:

Fig. 1 is a sectional elevation of a forced cirv Illustrative embodimentof the invention In the drawings character A denotes as a whole thelower portion of a furnace chamber bounded by four vertical walls,namely two side walls l0 and I2, front wall It and rear wall I6; andalso by a floor l8. Partition walls 20 and 22 within said lower furnaceportion A extend from side to side and from the floor IS upwardlydividing furnace portion A into primary compartments a, b and secondarycompartment c, the outer primary compartments 0, and b respectivelycommunicating with secondary central compartment 0 by way of opening 24adjacent wall l2 and opening 26 adjacent wall l0. Roof 28 forms the topboundary of compartment 0. and roof 36 forms the top boundary ofcompartment 1). Openings 24 and 26 extend between floor It and roofs 28and 30 respectively, or some portion thereof.

Compartment 0 is left open at the top to facilitate discharge ofcombustion gases from lower portion A of the furnace chamber throughopening I9. Outer side walls l0 and I2 and partition walls 20 and 22 areextended in an upwardly direction to form together with roof 3| theboundary of the upper portion B of said furnace chamber, this upperportion B being an extension of secondary compartment 0 and containing0]: communicating by way of gas discharge opening 31 with heat absorbingsurfaces which in the illustrative installation represented includehightemperature superheater section 0, reheater section D,low-temperature superheater section E, and upper and lower economizersection F and G respectively.

The furnace side of outside walls I0, [2, l4 and I6 and also partitionwalls 20 and 22 are equipped with vertical wall tubes 25 (see Fig. 2particularly) which are organized in communication with the forcedcirculation system of the steam generating unit in the following manner:

The forced circulation pump I receives water from drum J by way ofconduit K and discharges under pressure through conduit L, strainer Mand tubes N into lower side wall headers O and through tubes V to frontwall header P. There are two headers 0, one on each side of the unitfeeding water wall tubes 25 of furnace side wall In and [2 respectively.These water wall tubes extend from headers O upwardly to upper waterwall headers Q of which there are also two, one on each side of theunit. Some of the water flowing through these water wall tubes isevaporated into steam and a mixture of water and steam is dischargedfrom headers Q into drum J by way of connecting tubes R therebycompleting identical forced circulation circuits for these two sidewalls In and I2.

A portion of the water entering lower water wall header P flows upwardlythrough the water wall tubes 25 of front furnace wall l4 thencehorizontally over roof 28 downwardly through tubes of partition wall 20and upwardly through tubes on the other side of this wall continuingalong front wall 2| of upper portion B of furnace chamber into drum Jthereby completing the front wall circuit of the forced circulationsystem. Those of the tubes of roof 28 located in line with opening 24will of course turn up at the upper border 33 of opening 24 and continueto form front wall 2 l,

The remaining portion of the water entering header P proceeds alongtubes forming floor l8, up through wall I6, horizontally over roof 30thence down partition wall 22 and up on the other side and continuingupwardly to form rear wall 23 of upper furnace portion B, thencehorizontally along roof 3| of upper chamber B back to drum J therebycompleting rear wall circuit of the illustrative installations forcedcirculation system. Here again those tubes of roof 30 which lie oppositeto opening 26 will continue downwardly in the plane of partition wall22, turn to form the upper edge 35 defining opening 26, hence flowupwardly to join the remaining tubes of partition 22 in forming rearwall 23.

While water passes through front wall circuit and through rear wallcircuit some of it will be evaporated and a mixture of steam and waterfrom these circuits is collected in drum J together with steam and watermixture from aforementioned side wall circuits. Steam separation,washing and drying in a conventional manner takes place in drum J,whereupon the steam passes from drum J via drum T (if desired) andconduits 29 into and through superheaters E and C and thence to outletheader U.

primary air is delivered from an outside source (not shown) to burners32 arranged in a vertical row in the front portion of side wall I!) ofcompartment a and to burners 34 arranged in a vertical row in the rearportion of the side wall [2 of compartment b and discharged at highvelocity into these furnace compartment to be burned therein. Secondarycombustion air may be admitted into the furnace by way of rows of airnozzles 36 and 38 vertically arranged in the furnace compartment cornerson each side of the vertical burner row 32 and 34 respectively or in theusual manner through the burners 32. In the illustrated installationfuel is burned at a high combustion rate in both compartments a and b.Burners 32 and 34 impart a rotating turbulent motion to the fuel and airmixture while discharging same into the furnace chambers a and 1).Secondary air emitted from air nozzles 36 and 38 impinges on saidrotating fuel streams creating additional turbulence and thereby aids inthe combustion process.

In the operation of the installation illustrated the gas temperature isnormally maintained in compartments a, b and 0 above the fuel ash fusiontemperature and combustion is expected to be completed by the time thegas leaves compartment 0. Due to the impact of furnace gas against thewalls II and I2, 20 and 22 at the turns 24 and 26 ash in a fluid statecollects on these walls and flows to the bottom I8 of the furnaceforming a slag p001. Two circular openings 40 are provided inthe floorH! of compartment 0 to facilitate drainage of molten ash into slag pit Hfrom which the fluid ash can be removed by any known conventionalmethod.

The air supplied to the furnace both as primary and secondary combustionair is preferably preheated a substantial amount to speed up theignition of the fuel. The proportion and size of the fuel burningcompartments a and b in conjunction with the high combustion rate issuch as to impart a considerable velocity to the combustion gasapproaching and passing through openings 24 and 26 into intermediatefurnace compartment 0. A change of direction of flow of 180 deg. forcedupon the gas stream by partition walls 20 and 22 facilitates theseparation of suspended slag droplets from the outgoing gas and alsoretards the passing of combustible from furnace chambers a and b. Sinceone object of my A characteristic feature of a forced circulation designis the use of orifices installed in the var ious circuits, preferably atthe inlet to the water Wall surfaces, for the purpose of adjusting theflows of water through these circuits to variations in heat absorptionand circuit flow resistance. Accordingly in the preferred embodimentillustrated in Figs. 1 and 2 orifice plates (not shown) are installed inthe tube ends of side water walls In and I2 at their junction withheaders O and in the tube ends of front wall l4 and floor [8 at theirjunction with header P. This provision insures a controlled supply ofcooling water to all circuits in proportion to length and heatabsorption and greatly contributes to elimination of furnace tubefailures at high combustion rate operation by permitting the use ofsmall diameter thin wall tubes. 7

Solid fuel in relatively finely divided form (crushed or pulverized) andmixed with carrier or invention is the separation of liquid slag fromthe furnace gas primarily by impinging of the gas upon the furnacewalls, a high velocity of the furnace gas passing through the furnacecompartments a, b and c is essential, so that the combined action ofimpact and of change in direction of flow causes effective separation ofthe liquid slag droplets and solid particles from the gas stream.

During operation the Vertical furnace walls l4, I6, 20 and 22 will becovered with a thin layer of liquid slag due to the turbulence createdby rotative discharge of fuel and the secondary air streams issuing fromthe corners adjacent the burners and the high temperature existing incompartments a and b. The portion of wall 12 and wall 22 enclosing inpart compartment a and 0 respectively and the portion of wall [0 andwall 20 enclosing in part compartments 1) and 0 respectively are as setforth above, primarily instrumental in collecting ash by impingement ofthe gas stream upon their surfaces. This accumulation of ash is enhancedby centrifugal action due to change in direction of the gas flow.

While the gas streams are entering compartment 0 an upwardly change indirection of flow is imparted causing the stream to enter through gasdischarge opening IS th upper portion B of the furnace chamber where theexposed water walls effectively cool the gas before it proceeds to flowthrough ga discharge opening 31 and over heating surfaces C, D, E, F andG giving up heat to these heat absorbing surfaces and leaving the steamgenerating unit by way of gas duct X. By adjusting dampers S the gasflow over superheater E is controlled, thereby serving as a means forregulating superheated steam temperature.

With the described method of fuel burning combustion of the fuelparticles will proceed at a high rate. Portions of the furnace walls l0,l2, I4, I6, 20 and 22 covered with heavy deposit of molten slag willalso collect heavier unburned coal particles imbedded therein byimpingement and centrifugal force. A stream of oxygen-rich furnace gasis continuously scrubbing these wall portions at high velocity and ithas been demonstrated that under such conditions coal deposited on themolten slag surface will become completely burned. Since the lowerportion of the furnace chamber will be operated at temperatures abovethe fusion temperature of the ash and collect most of the ash, the gaswill be quite free of ash and sufficiently cooled before leaving theupper portion B of said furnace chamber through gas discharge opening37, so that any ash still remaining in the furnace gas will be in a drystate. Dry ash which falls or is removed from the walls of the upperfurnace chamber and accumulates at the bottom of compartments 0 willmelt and also flow to the slag openings 40.

The Problem which invention solves Summarizing the problem, the highsuperheated steam temperature demanded by modern steam power generatingpractice requires in most cases a high furnace outlet gas temperaturewhich may well equal or exceed the ash fusion temperature of many coalsmined in the United States and other countries. In the operation ofconventional pulverized coal fired furnaces where the gas leavingtemperature exceeds the ash fusion point of the coal, a considerablepercentage of the ash in the fuel is carried in suspension in the gasstream leaving the furnace in the form of tiny liquid ash droplets. Uponcontact of these gases with convection heat absorbing surfaces, theaforesaid suspended slag droplets will solidify and deposit on said heatabsorbing surfaces causing reduction in the transfer of heat from gasesto slag covered surfaces and eventual costly shutdown of the steamgenerating unit for cleaning purposes.

This problem of eliminating slagging difficulties in convection heatingsurfaces is being approached from several directions. One line of attackis directed at the lowering of the furnace outlet gas temperature to avalue safely below the ash fusion temperature of the coal. Other effortsare directed towards eliminating the greater portion if not all of theash in the combustion chamber before the gases reach any convectionheating surface, in other words disposing of the ash through an openingin the furnace bottom while the ash is still in a fluid state.

As previously indicated my invention is concerned with this latterapproach.

While in the prior art, in working along this line, attempts have beenmade to arrive at a solution by various designs of slagging furnaces,these attempts have been only partially successful. Some conventionaldesigns of slagging bottom furnaces of high capacity (in theneighborhood of 1,000,000 lb. steam per hour) have a relatively lowoverall heat release per cubic foot of furnace volume. The ratio offurnac heating surface to furnace volume being low in large units, thetotal furnace volume therefore is far out of proportion and inconsistentwith economical furnace design practice. Gas velocity in the furnace isvery low and the contact of combustion gas with furnace heating surfacevery limited.

If a higher heat liberation is attempted in such a conventional furnacethe gas temperature leaving the furnace chamber increases beyond safelimits, unless furnace heat absorbing surfaces are added by furtherincreasing the volume of the furnace or by adding more heating surfacesuch as partition walls without increasing the volume of the furnace.Attempts in the prior art had been made to follow the latter course,however difficulties were encountered in sufliciently cooling theseadditional heating surfaces by water circulation. These surfacestherefore had to be covered with a refractory layer to prevent theirdestruction. My invention has overcome this difficulty by adapting awell known mode of forced circulation to a uniquely designed multiplechamber furnace characterized by an exceedingly high combustion rate inthe primary portion of the furnace.

The proposed design allows the use of relatively small diameter thinWalled tubes in contrast to relatively large diameter heavy walled tubeswhich must be used in natural circulation design in order to obtainadequate fluid flow.

Some research was also directed at separating the ash suspended in theproducts of combustion by the action of centrifugal force. M inventionnot only uses centrifugal force but in addition it employs a separationmethod entirely new and novel in the art of burning slag forming fuels.This novel method consists in impingement of a high velocity gas stream,carryin slag droplets, on slag covered partition walls whereby said slagdroplets having a low Viscosity by virtue of their high temperaturesplatter against the water cooled wall surface, adhere thereto due tothe wall cooling effect lowering their viscosity, and form a viscouslayer of running slag which continuously retains other slag dropletsbeing hurled against them.

The aforesaid effect is obtained in my preferred embodiment of theinvention by confining the high velocity gas stream between two wallsand forcing this stream to abruptly change direction by substantiallydeg. entering another confining channel formed by furnace walls, therebycausing the heavier-than-gas slag droplets to separate and splatteragainst the wall surfaces circumscribing the turn.

It can be appreciated by anyone skilled in the art that these surf-acestake a considerable punishment and failure of these furnace wallsWithout protective refractory coating would occur in a relatively shorttime. However by employin the earlier-disclosed forced circulation meanswith such high combustion rate operation I have succeeded in coolingthese trouble spots continually and effectively.

Advantages obtained by invention Among the advantages obtainable by theherein-disclosed unique organization of my invention, mention may bemade of the following:

First advantaiga fhe principal characteristics of my invention such asthe high velocity of the combustion gases (flowing from outer chambers aand 1) into central chamber and thence upwardly) together with theaccompanying abrupt changes in direction, and consequent impingement ofthose gases on viscous and absorbing slag coatings (within the lowerfurnace portion A), results in an extremely high slag elimination efficiency thereby minimizing slagging accumulations on subsequentconvection heating surfaces (within the upper furnace portion B andthereafter) Second advantage-The forced circulation water cooled furnacepartition walls (including and 22) uniquely arranged to compress thegases into high velocity multiple streams (into and through centralchamber 0) and also to form high combustion rate multiple firin chambersw-b makes it possible to increase the surfaceover-voluine ratio of thefurnace to such a marked degree that considerable savings in first costcan be realized without incurring a risk of excessive maintenance coston water walls when in operation.

Third advantage-Em unique combination of my invention in using forcedcirculation circuits in a high combustion rate, high velocity, ashslagging multiple furnace allows the designer complete freedom inarranging furnace heating surfaces such as partition walls and firingchambers for maximum ash separation efficiency without at the same timehaving to be concerned with and being limited by Water circulationproblems which are ever present in the conventional natural circulationboiler.

Fourth advantage.Combining forced circulation circuits with slaggingbottom, multiple chamber furnace affords the advantage, residing in thefree use of furnace wall tubes of relatively small diameter permittingthe employment of a proportionally thinner tube wall for a given steampressure. In large diameter tubes having a relatively thick wall, suchas required in natural circulation design, excessive thermal stressesresulting from a high temperature difference between outside and insidesurface of the tubes, contribute greatly to failure of furnace tubes. Athinner tube wall results in a lower temperature difference reducingthermal stresses considerably and thereby minimizing tube failures.Small diameter tubes are permissible in forced circulation boilersbecause a positive and sufficient flow of water through the tubes isassured at all times regardless of size, shape and location.

Fifth advantage.ln addition forced circulation design in conjunctionwith my uniquely arranged partitioned multiple chamber furnace affordsoperation of the steam generating unit over a wide load range withoutundue difficulties and with high ash collection efliciency even at verylow loads. Thus low-load operation is accomplished by firing fuel intoone chamber only maintainin in the gas passages a high impingingvelocity essential for efiicient ash removal and at the same timeproviding an adequate flow of fluid through all water wall heatingsurfaces including those in the unfired chambers thereby preventingpossible damage to those water cooled tubes.

My design also affords a higher superheated steam temperature at lowload, than can be obtained with conventional design, by reducin theeffectiveness of some of the furnace heating surface when operating withone firing chamber only.

Sixth adcantage.-The herein-disclosed novel method of burningash-containing fuel in crushed or pulverized form at high combustionrates in the presence of high velocity air streams and confining theresultant products of combustion between slag covered partition wallsspaced and arranged so as to cause a high velocity flow and abruptchange of direction of the gas stream, not only results in theseparation of ash droplets from said stream but also causes heavierunconsumed coal particles to be ejected and thrown against the stickyash coating of the walls at the turn and then burned therein by thescrubbing action of the oxygen-rich gas stream. This effectivelycontributes to reduce combustible loss in fly ash thereby increasing theoperating efficiency of the steam generator.

Seventh adt-antage.--Conventional slagging bottom furnaces cannot beoperated efficiently with coarsely ground coal because of excessivecombustible loss. My design however permits the burning of comparativelycoarsely ground or crushed coal since my method of slag elimination byimpinging on slag covered furnace and partition walls at the same timecauses rapid consumption of coal particles hurled against and imbeddedin said. slag coating and by a continuous consequent scrubbing withoxygen-rich gas.

Thus, from the foregoing, it can be appreciated by those skilled in theart how a long felt unfulfilled need in burning ash-containingfinelydivided fuel in an efiicient and economical manner has beensatisfied by the above described invention herein disclosed.

While I have illustrated and described a furnace with burners 32 and 34firing in directions perpendicular to walls 10 and [2 these burners alsocan be arranged to fire in other ways; i. e., they may be arranged forcorner firing as indicated by nozzles 36 and 38 of Fig. 2. Also it isapparent that other modifications may be made in the construction of theinventive apparatus shown such as changes in size, proportion and numberof furnace compartments and partition walls.

Although the above described preferred embcdiment of my invention ispresented as being applied to a forced circulation boiler, my uniquelyarranged multi-chamber furnace, employing partition walls for theexpress purpose of increasing the heating surface as Well as forcing thecombustion gas into flow paths to eliminate within the lower furnacemost of the ashes carried by said gas, can also be applied to a steamgenerating unit designed for natural circulation.

Therefore it will be understood that while I have illustrated anddescribed herein only one form of apparatus embodying the invention,those skilled in the art will appreciate that changes and modificationssuch as those aforementioned may be made in said disclosed apparatuswithout de+ parting from the spirit and scope of the invention ascharacterized by the claims.

What I claim is:

v 1. In apparatus for burning slag forming fuel, the combination of afurnace chamber of generally rectangular cross section defined by firstand second side walls, front wall and rear wall, floor and roof; firstand second spaced and generally vertical partitions extending crosswiseof said chamber respectively from said first side wall and from saidsecond side wall and dividing the chamber into three parallelcompartments including a central compartment sandwiched between a frontouter compartment and a rear outer compartment; means forming a gasdischarge opening in the roof of said central compartment substantiallycoextensive with the width and length of that compartment; meansadjacent the second-Wall side of said first partition forming a firstunobstructed gas communication openin from said front outer compartmentinto said central compartment; means adjacent the first-wall side ofsaid second partition forming a second unobstructed gas communicationopening from said rear outer compartment into said central compartmentwhich second opening is located on the opposite furnace chamber sidefrom said first gas communication opening; means for introducing a highvelocity stream of primary air and slag forming fuel in suspension intothe portion of said front outer compartment that is remote from saidfirst gas communication opening leading to the central compartment;means for introducing a high velocity stream of primary air and slagforming fuel in suspension into the portion of said rear outercompartment that is remote from said second gas communication openingleading to the central compartment; means for also introducing secondaryair into the aforesaid fuel-entering portion of said front outercompartment and into the aforesaid fuel-entering portion of said rearouter compartment to assist in combustion of the said slag forming fuelburned in those two outer compartments, whereby there is created in saidfront outer compartment a high velocity stream of combustion productsflowing towards said first gas communication opening and in said rearouter compartment a high velocity stream of combustion products flowingtowards said second gas communication opening thus forcing those gaseousproducts of combustion to make turns of substantially 180 degrees assame pass into said central compartment; and inner exposed metallicsurface lining the walls, roof, floor and partitions of the aforesaidthree compartments, said central compartment containing only heatabsorbing surface composed of said inner metallic wall surface, therebyaffording an unobstructed passageway for the flow of gases therethrough.

2. In a steam generator, the combination of a first outer compartmentand a second outer compartment, said compartments being spacedlypositioned side by side; an inner compartment sandwiched between saidfirst outer compartment and said second outer compartment, said innercompartment having a first wall in common with said first outercompartment, a second opposite wall in common with said second outercompartment, two opposing end walls and a roof; means in said firstcommon wall and adjacent one of said two end walls for providing alateral passage from said first outer compartment into said innercompartment; means in said second common wall and adjacent the other ofsaid two end walls for providing a lateral passage from said secondouter compartment into said inner compartment; nozzle means fordischarging fuel and air streams for combustion into that portion ofeach of said outer compartments which is remote from said lateralpassage thereof; inner exposed metallic surface lining the walls of theaforesaid inner compartment, said metallic wall surface constituting theonly heating surface contained within said inner compartment, therebyaffording an unobstructed passageway for the flow of gases therethrough;means forming a gas uptake passage through the roof of said innercompartment; and heat absorbing surfaces located in said gas up-takepassage, whereby the stream of combustion gases being discharged intosaid up-take passage from said inner compartment is substantially freeof temperature stratification while passing over said heat absorbingsurfaces.

WARD S. PATTERSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,731,428 Lundgren Oct. 15, 19291,738,636 Caracristi Dec. 10, 1929 1,966,054 Wheeler, Jr July 10, 19342,204,350 Frisch June 11, 1940 2,258,235 Barnes Oct. 7, 1941 2,285,442Kerr June 9, 1942 2,357,303 Kerr et al Sept. 5, 1944 FOREIGN PATENTSNumber Country Date 71,857 Sweden Feb. 13, 1928 833,423 France July 18,1938

